Hi @fusari,
The SCALED_IMU* messages provide their acceleration values in mG, which stands for milli-gravity (1000 x 9.80665 m/s2) - when the vehicle is stationary the zacc should be approximately -1000, due to the downwards force of gravity on Earth.
The MAVLink specification does not include units for the RAW_IMU messages, so they could technically be specific to the implementation or the sensor in use.
From the ArduPilot source code it seems like ArduPilot firmwares present the IMU data with consistent scaling, via the messages
RAW_IMU(withid=0) for IMU 0SCALED_IMU2for IMU 1 (for the sensors that exist)SCALED_IMU3for IMU2 (if there are any relevant sensors)
For our most common flight controller boards:
| MAVLink message | Navigator | Pixhawk |
|---|---|---|
RAW_IMU |
Acc / Gyr: ICM-20602 Mag: MMC5983 |
Gyr: L3GD20H Acc / Mag: LSM303D |
SCALED_IMU2 |
Mag: AK09915 | Acc / Gyr: MPU 6000 |
I believe the relevant scaling and offsets should already be applied, but you can query the values of the INS_ACCOFS_X/Y/Z and INS_ACCSCAL_X/Y/Z parameters if you want to.
Note that because the z-direction is not expected to have a 0 value, if the flight controller is at all rotated about its pitch and/or roll axes then the x and y accelerometer readings will be non-zero as well, due to gaining some component from the force of gravity.
Two programs generally cannot be connected to the same port on a computer - if you need both Python and QGroundControl to be connected to your vehicle at the same time then you should set up an additional MAVLink Endpoint for Python to connect to.
Note that if a joystick is connected to QGC it will be sending continual joystick messages, so if you also try to send some control messages from Python at the same time then they will be fighting against each other.